Use of titanium article support for hot dip galvanizing apparatus



Sept. 16, 1958 R. H. BREWER USE OF TITANIUM ARTICLE SUPPORT FOR HOT DIPQALVANIZING APPARATUS Filed March 16, 1954 T '2 c l I v E m H HT W M; Mk 0 1' W W 0 0A A m w I l AQ W J M v L k F1 J K 1/ WW w M n r. am Hm i 1F. 6 oz 5% 4 WW d M M I I I I I I .|.l| I I I 7 7 Q 8 United StatesPatent USE OF ARTICLE SUPPORT FOR HOT DIP GALVANIZING APPARATUS RichardH. Brewer, Warren, Ohio, assignor to Republic Steel Corporation,Cleveland, Ohio, a corporation of New Jersey Application March 16, 1954,Serial No. 416,665

1 Claim. (Cl. 117-51) The present invention relates to hot dipgalvanizing apparatus, and particularly to structure for supportingarticles being galvanized as they are immersed in a bath of molten zincand in other baths, such as those commonly used in typical galvanizingprocesses.

In a conventional hot dip galvanizing process, the articles to begalvanized are placed on supporting structures, commonly hooks, attachedto a suitable conveyor mechanism. The conveyor mechanism carries thearticles sequentially over a series of tanks containing preliminary bathtreatment mixtures and then over a tank filled with molten zinc. As theconveyor passes over each tank, the articles are lowered into the tank,both the articles and the supporting structure attached to the conveyorbeing then immersed in the liquid in the tank. A typical series ofpreliminary tanks includes: a pickle tank containing a solution ofdilute sulfuric acid; a hot water rinse tank; and a flux tank containinga hot solution of zinc ammonium chloride. The hot zinc bath follows thisseries, and a final water rinse tank completes the apparatus.

Considerable time and eifort have been expended in the past in an efiortto find a material which may be used to construct the hooks or othersupporting members mounted on the conveyor and which support thearticles being galvanized. These hooks are subjected to repeated cyclesof immersion in highly corrosive chemical solutions at hightemperatures, followed by exposure to air and subsequent immersion inmolten zinc. All these immersions and exposures tend to corrode and wearaway the material of the hook or other supporting structure at a rapidrate. Certain materials have been found, e. g., Monel metal, whichresist corrosion satisfactorily, but which are rapidly coated by themolten zinc. This zinc coating dissolves in the next passage through theacid 'bath, resulting in rapid contamination of the acid and consequenthigh acid consumption. Prior to the present invention, no material wasknown which would resist I corrosion and which would not pick up zinc.

which must be immersed in these solutions and in the molten zinc. Therate of corrosion of the solutions on these parts is definitely known,and the parts are designed with a suflicient thickness to give a certainduration of usable life. At the end of that time, the parts arediscarded and replaced with new ones.

The metal titanium has been known for some time as having high corrosionresistance at low temperatures, but it has also been known as being veryactive chemically at high temperatures, and for that reason has beenconsidered unsuitable for any application where it might be subjected totemperatures such as that encountered in exposure to molten zinc at 860F. Furthermore, tests of titanium continuously exposed to molten zinchave shown that after several (-to 20) hours exposure, the titanium isattacked by the zinc, initially by the formation of a zinc coating.After a few more hours, an active corrosive attack takes place. Suchtests tend to confirm the sus- 2,852,410 Patented Sept: I6; 1958 picionthat titanium would be unsuitable for use in hot dip galvanizingapparatus:

However, a number oftestshave now-beenmadewith titanium supportingstructures inconnectiom with timetioning-"hot dip galvanizing apparatus:It has been" found that, contrary'to all expectations; titaniumjhooksprepared for such purposes do not 'pick up-zinc andare' not corroded,even after repeated passage through the galvanizing cycle. The reasonforthis unexpected resistance to coating by' the zincand to corrosionhas notyet been definitely determined, but it isbelievedthat some sortof passivation actiontakesplace; either-as a resultjofdip= ping thetitanium into the pickling and flux solutions, or as a result of theexposure of the titanium to the air between dips in the molten zinc.

In any event, regardless of theory, experience has shown that titaniumparts when used in intermittent exposure to the acid and zinc baths ofthe galvanizing line, will withstand a far greater total time of zincimmersion than in a situation of continuous immersion, as mentionedabove.

In the accompanying drawings:

Fig. 1 is a somewhat diagrammatic plan view of a hot dip galvanizingline to which the present invention may be applied;

Fig. 2 is an elevational view of a simple hook formed of titanium andusable in the hot dip galvanizing process in accordance with the presentinvention, and

Fig. 3 is a perspective view of a basket which may be formed of titaniumfor use in the galvanizing cycle to support parts being galvanized.

Referring to the drawings, Fig. '1 shows a pickle tank 1, a rinse tank2, a flux tank 3, a galvanizing pot or tank 4, and a cooling tank 5.

A conveyor (not shown) runs along a path connected by the dotted line 6and extends over each of the tanks 1 to 5. The conveyor includesequipment of a type well known in the art for lowering articlesdepending from the conveyor into the respective tanks as the articlesupporting structures pass over the tanks. The article supportingstructure may take the form of a hook 7 as shown in Fig. 2, having athread 7a on its upper end for attachment to the conveyor. The hook 7 isformed of titanium, for example titanium metal in forms which arecommercially available and which may include minor alloying ingredientsconventional in such metal.

'In a typical process, the book 7 and the articles to be galvanizeddepending from it are subjected to the following cycle:

(1) Immersion for 12 minutes in the pickle tank 1 containing a sulfuricacid solution having a strength of 12% by volume and maintained at 190F;

'(2) A quick dip in a hot water rinse 2 also maintained at 190 F.;

(3) A quick dip in a flux tank 3, containing solution of zinc ammoniumchloride, also maintained at 190 F. (This solution contains 300 poundszinc ammonium chloride to gallons of water); i

(4) Three minutes drying in the air;

(5) Immersion in the molten zinc pot for thirty seconds. The zinc ismaintained at a temperature of 860 F. and the top of the tank is coveredwith a 1" blanket of "ammonium chloride;

'( 6) A clip in cooling water at 99 F.

It has been found that the titanium hook used in the cycle describedabove shows no corrosion and no deposition of zinc on it even afterrepeated operation through the cycle.

Fig. 3 shows a basket 8 which may be formed of titanium and used tosupport parts being carried through a galvanizing cycle. The inventionis equally applicable to other working parts which are subjectedintermittently t0 the conditions in the several tanks of the galvanizingapparatus. Such parts to which the invention is applicable include, forexample, cradles, chains or tools.

-I claim:

In a method of hot dip galvanizing, which includes the steps of moving asupport repeatedly through a cycle including the steps of placing anarticle to be galvanized on the support, immersing at least a part ofsaid support and the article supported thereon successively in a pickletank containing dilute sulfuric acid, a flux tank 10 containing asolution of zinc ammonium chloride, and a tank containing molten zinc,thereby galvanizing the artiale, and removing the galvanized articlefrom said support; the improvement which comprises using supports formedof titanium so that said supports may be moved repeatedly through saidcycle without being attacked sub- References Cited in the file of thispatent UNITED STATES PATENTS Watrous July 13, 1920 Pheem et al Aug. 29,1950 OTHER REFERENCES 15 March 15, 1949, pp. 9, 13, 14, 19, 20 and 21.

